PROJECT SUMMARY: Chemistry/Structural Core B Ewing sarcoma, a solid tumor that forms in bone or soft tissue, affects mostly children, adolescents and young adults. Currently, approximately 70% of patients respond well to the standard of care, but patients with metastatic or recurrent Ewing sarcoma have survival rates below 30%. The broad goals of the Center for Therapeutic Targeting of EWS-oncoproteins (Center) revolve around the need to better understand the basic biology of Ewing sarcoma, and translate these insights into targeted therapeutics. The goals of the Center are distributed across three Projects that will examine different aspects of the biology of EWS-oncoproteins and make discoveries needed to facilitate development of targeted therapeutics strategies. The objective of Core B is to provide chemistry and structural biology expertise that will facilitate translation of new basic biology into innovative targeted therapeutic strategies. The central hypothesis is that the better understanding of EWS fusion oncoproteins degradation (Project 1), their interactomes (Project 2), and mechanisms that govern aberrant transcription in the disease (Project 3) will reveal specific points for targeted therapeutic intervention, and that Core B will be able to bridge biology with chemistry and pharmacology by developing new small molecules and providing structural biology framework for understanding biological processes. The rationale for Core B is that identification of the mechanism(s) used by EWS fusion oncoproteins to govern transcriptional regulation and epigenetic reprograming in Ewing sarcoma will provide molecular information sufficient to develop small molecule inhibitors and degraders. Core B specific aims will test the following hypotheses: (Aim1) small molecule transcriptional inhibitors and degraders will repress core regulatory circuits (CRC) and tumor growth in Ewing sarcoma (Project 3); (Aim 2) structural characterization of key domains of EWS-FLI1 interacting proteins will open new windows for targeted therapeutic intervention (Project 2); (Aim 3) degrader molecules for EWS-FLI1 and EWS-ERG fusion oncoproteins will be a feasible and meaningful anti-Ewing sarcoma strategy (Project 1). Upon conclusion of the work in the Center, we will understand the role of EWS-oncoproteins in Ewing sarcoma and have viable lead molecules for development of targeted therapies, the aspect of the Center?s activities to which Core B will contribute in an essential capacity. Overall, these efforts are significant because they combine multidisciplinary scientific expertise required to address an unmet medical need. The significance of Core B efforts resides in accelerating translation of basic insights into small molecule probes and lead compounds, which in turn will enable further basic and clinical discoveries. The proposed Core B research is innovative because we will explore the use of small molecule degraders, a novel pharmacological modality, in the context of a disease that is driven by proteins that are considered to be undruggable.